The present invention relates to a novel hydraulically actuated dual fuel injector for an internal combustion engine. More particularly, the application pertains to a hydraulically actuated injector for injecting controlled quantities of a first fuel and a second fuel into an internal combustion diesel engine at different times.
Because of its ready availability, low cost and potential for reducing particulate emissions, natural gas is a promising candidate for fuelling diesel engines. Known methods for converting a conventional diesel-fuelled engine (that is, a compression-ignition engine) to consume natural gas fall into three general approaches:
(1) Converting the engine to a stoichiometric or lean-burn spark-ignition engine;
(2) Converting the engine to natural gas using a xe2x80x9cdual-fuelxe2x80x9d technology, in which the natural gas is mixed with all of or with a portion of the intake air and is ignited by diesel fuel injected at the end of the compression stroke; and
(3) Converting the engine to directly inject the natural gas fuel into the combustion chamber, with a source of ignition.
The differences between these three approaches are elaborated upon in the more detailed discussions of these methods in the following paragraphs. However, the preferred method, is the direct injection method because it is the only method that preserves the inherent favorable operating characteristics and high efficiency of conventional diesel-fuelled engines.
A conventional diesel-fuelled engine can be converted to natural gas by injecting natural gas with the intake air and allowing the mixture to enter the chamber through the intake valve. The mixture, stoichiometric or lean, can then be ignited near top dead center using spark plugs. However, to avoid detonation of the mixture, the compression ratio of the engine must be reduced. A reduction in compression ratio is accompanied by a reduction in efficiency, or equivalently by an increase in fuel consumption. Furthermore, to maintain the strength of the mixture under all conditions, the intake air must be throttled, causing pumping losses and further increasing the fuel consumption required to maintain equivalent power. These losses are especially pronounced at low or part load levels, which are the predominant operating conditions of automotive engines. Typically, the conversion of diesel engines to stoichiometric or lean-burn combustion of natural gas with spark plug ignition offers a considerable reduction in harmful emissions, but also leads to an increase in fuel consumption.
In this method, the natural gas is generally admitted in the intake air and enters the combustion chamber through the intake ports or valve. The mixture is ignited near top dead center by the injection of pilot diesel fuel. There are, however, fundamental complications with this method:
1. At low load, with unthrottled diesel operation, the gas fuel and air mixture is too lean for satisfactory combustion. The fuel consumption increases under these conditions and the hydrocarbon emissions also increase. Remedies to this situation include:
a. Reverting to diesel fuel operation at low loadsxe2x80x94in some applications where substantial part load conditions exist this remedy defies the purpose of the fuel substitution.
b. Throttling of the intake air, which is complicated when the engine is equipped with turbochargers because of the danger of compressor surge (although with modern electronic-controlled waste gates this may be avoidable). In any case, such throttling removes an inherent advantage of diesel operation.
c. Skip-firing, which consists of not firing the cylinders at each cycle but rather at every other cycle. This method does not usually permit smooth engine operation, particularly on 4 cylinder engines, and is usually too unstable for idling, requiring straight diesel operation.
2. Because a premixed fuel-air mixture exists during the compression, there is a danger of knocking (an uncontrolled combustion of the mixture), with potential engine damage. Thus, reduction in compression ratio may be required. If a reduction in compression ratio is chosen, the engine efficiency is compromised. If the compression ratio is maintained, the amount of natural gas used under each condition must be limited such that the mixture formed is not prone to knocking. This means that more diesel fuel must be used to sustain high load cases.
This pilot ignition method and the previously discussed spark ignition method are not well suited for 2-stroke engines because a substantial amount of the intake charge flows out the exhaust valve in two-cycle engines and is wasted. To avoid this bypass, and to improve on the low load combustion characteristics, it has been proposed to inject the natural gas directly into the combustion chamber after all valves or ports are closed, but still at a relatively low pressure. This adds difficulty because a new injection system control is needed, modifications to the head or block are required, and metering the gaseous fuel and ensuring stratification is difficult.
So far as is known, this second method has been proven capable of maintaining the efficiency over a wide range of load and speeds only by retaining a substantial amount of diesel fuel to compensate for the above problems.
The great advantage of directly injecting fuel into the engine cylinders in diesel operation is that it permits efficient and stable burning over the whole load range. This is because the burning occurs in local regions in which the fuel-air ratio is within the prescribed flammability limits. When a gaseous fuel such as natural gas is substituted for diesel fuel, the gaseous fuel has an advantage over diesel fuel in that it does not require atomization into micron-sized droplets and thus does not require very high injection pressures. For diesel injection, pressures as high as 1000 atmospheres are required for most efficient operation. For a gaseous fuel such as natural gas, pressures of 200 atmospheres are satisfactory. The principal difficulty with the direct injection of natural gas is that natural gas will not self-ignite, as diesel fuel does, at the typical temperature and pressure range of a diesel engine. To overcome this difficulty, another source of ignition must be provided. Examples of ignition sources are: (a) a small quantity of self-igniting pilot diesel fuel injected with or separate from the natural gas, and (b) glow plugs or hot surfaces and the like. For economic reasons, it is desirable to limit the necessary modifications to the engine. In that respect, an advantageous design employs a dual-fuel injector that fits in the same opening as a conventional single-fuel injector so that both a pilot fuel and a gaseous fuel can be injected into the combustion chamber without modifying the engine block or cylinder head.
Successful operation of large bore diesels with direct injection of compressed natural gas has been demonstrated in North America, as discussed in the following publications:
1. J. F. Wakenell, G. B. O""Neal, and Q. A. Baker, xe2x80x9cHigh Pressure Late Cycle Direct Injection of Natural Gas in a Rail Medium Speed Diesel Enginexe2x80x9d, SAE Technical Paper 872041;
2. Willi, M. L., Richards, B. G., xe2x80x9cDesign and Development of a Direct Injected, Glow Plug Ignition Assisted, Natural Gas Enginexe2x80x9d, ICExe2x80x94Vol. 22, Heavy Duty Engines: A look at the Future, ASME 1994; and
3. Meyers. D. P., Bourn, G. D., Hedrick, J. C., Kubesh, J. T., xe2x80x9cEvaluation of Six Natural Gas Systems for LNG Locomotive Applicationsxe2x80x9d, SAE Technical Paper 972967.
Meyers et al. at the Southwest Research Institute demonstrated the superiority of the direct injection of natural gas over other means of fuelling a locomotive engine with natural gas. The direct injection of natural gas led to the best thermal efficiency for the targeted reduction of nitrogen oxide emissions. They used two separate injectors to accomplish the injection of the two fuels. The gas injector was hydraulically actuated and electronically controlled and was mounted at an angle in the combustion chamber. The original diesel fuel injector was used, but with smaller holes to reduce the amount of diesel pilot fuel injected.
The work by Wakenell et al. carried out at Southwest Research Institute, involved direct injection of natural gas into a large bore (8.5 inch) 2-stroke, locomotive diesel engine. The natural gas was stored in liquid form (LNG), then pumped to high pressures of 5000 psi (340 atm). Full rated power was achieved with less than 2% pilot diesel fuel (98% natural gas) and thermal efficiency was slightly lower than 100% diesel operation. The gas injector valve replaced the diesel injector and a small diesel injector was installed in the xe2x80x9ctest-cockxe2x80x9d hole in the cylinder head. The gas injector was hydraulically actuated, with an independent hydraulic pump supplying the high-pressure hydraulic fluid.
Willi and Richards at Caterpillar demonstrated the possibility of using glow plugs to ignite the directly injected natural gas in a diesel engine. The results indicated equal or better thermal efficiency and nitrogen oxide emissions and reduced particulate matter. The injector used for this application is a modified HEUI injector from Caterpillar (which is the subject of SAE papers 930270 and 930271 and inferentially in U.S. Pat. Nos. 5,181,494, 5,191,867, 5,245,970 and 5,143,291). The injector, designed for gas injection only, contains a mechanism to control the injection rate of the gaseous injection. Pressurized oil is supplied from a common pump, and is intensified within the injector. There appears to be no means for injecting a pilot fuel.
The following Norwegian publications disclose injection of gaseous fuel in diesel engines:
1. Einang, P. M., Korea, S., Kvamsdal, R., Hansen, T., and Sarsten, A., xe2x80x9cHigh-Pressure, Digitally Controlled Injection of Gaseous Fuel in a Diesel Engine, with Special Reference to Boil-Off from LNG Tankersxe2x80x9d, Proceedings CIMAC Conf., June 1983;
2. Einang, P. M, Engja, H., Vestergren, R., xe2x80x9cMedium Speed 4-stroke Diesel Engine Using High Pressure Gas Injection Technologyxe2x80x9d, Proceedings CIMAC Conf., 1987.
Einang et al. (1983), in Norway, conducted tests involving the direct injection of natural gas into a 2-stroke marine diesel engine through a separate gas injector, the original diesel fuel injector being used for pilot ignition. With 73% natural gas proportion, the thermal efficiency of the natural gas fuelled engine was slightly better than diesel fuelling. The NOx emissions were reduced by some 24%. No details of the gas injector were released. The subsequent work [1987] involved the direct injection of natural gas with pilot diesel fuel in a four-stroke engine. A combined gas/oil injection valve was used, but no details of that injector are disclosed in the publication.
In Finland, the following publication is of interest:
1. Verstergren, R., xe2x80x9cThe Merits of the Gas-Diesel Enginexe2x80x9d, ASME ICExe2x80x94Vol. 25-3, 1995.
Dual fuel injectors are not detailed in the Verstergren publication, but appear in a number of publications and patents discussed below.
From Japan and Denmark, the following publications are of interest:
1. Miyake, M., Endo, Y., Biwa, T., Mizuhara, S., Grone, O., Pedersen, P. S., xe2x80x9cRecent Development of Gas Injection Diesel Enginesxe2x80x9d, CIMAC Conf., Warsaw, 1987;
2. Biwa, T., Beppu, O., Pedersen, P. S., Grone, O., Schnohr, O., Fogh, M., xe2x80x9cDevelopment of the 28/32 Gas Injection Enginexe2x80x9d, MAN BandW;
3. Miyake, M., Biwa, T., Endoh, Y., Shimotsu, M., Murakami, S., Komoda, T., xe2x80x9cThe Development of High Output, Highly Efficient Gas Burning Diesel Enginesxe2x80x9d, 15th CIMAC Conference, Paris, 1983, Proceedings, vol. A2, pp. 1193-1216;
4. Fukuda, T., Komoda, T., Furushima, K., Yanagihara, M., Ito, Y., xe2x80x9cDevelopment of the Highly Efficient Gas Injection Diesel Engine with Glow Plug Ignition Assist for Cogeneration Systemsxe2x80x9d, JSME-ASME International conference in Power Engineering, ICOPE-93.
The Japanese work of Miyake et al. (Mitsui Engineering and Shipbuilding Co.) showed favorable results, with equivalent engine efficiency at 85% of engine load using 5% pilot diesel fuel in a large diesel engine (420 millimeter bore). Two injection systems are presented; the first one is the utilization of 2 separate injectors. In that instance, a gas injector design is discussed and is based on a hydraulically actuated needle. The source of hydraulic actuation is an engine driven actuator-pump. A single injector design capable of injecting both the pilot diesel fuel and the natural gas is also presented. The injector is also actuated by an external source of pressurized oil, and is based on concentric needles. However, the design is not well suited for smaller diesel engines, since the needle seats are not at the tip of the injector. This means that a substantial amount of fuel remains in the injector and can be injected late in the expansion stroke. This situation is not very important in an engine with high fuel consumption, but it leads to increased pollutant emissions and loss of efficiency in a smaller engine operating from idle to rated speed.
The same Japanese authors presented further refinements and tests in 1987. A new combined injector was presented based on two separate needle valves located upstream from the injector tip, one controlling the pilot diesel fuel and one controlling the natural gas. As mentioned above, this design is not well suited for smaller size engines, because of the amount of fuel trapped between the needle valve and the injector tip, resulting in late injection. Also, it is difficult to provide fine atomization of the pilot diesel fuel with a needle valve located away from the tip.
The Mitsui Engineering team also tested a system using direct injection of natural gas only with glow plug ignition. In this case, a gas injection valve was used, but the schematic diagram reveals little information about the needle valve, which is actuated by high-pressure oil supplied by an external pump.
The work of the Japanese and Danish team on the 28/32 Engine (MAN BandW Diesel and Mitsui) also featured a single injector capable of handling pilot diesel fuel and natural gas fuel. This time, the design was based on two separate needle valves located upstream from the nozzle. The design featured high-pressure oil as a means of sealing the high-pressure natural gas. The 28/32 engine is a fairly large bore (280 millimeters) engine used for generators and in marine applications. The actuating oil was also supplied from an independent pump. The injector design includes a needle valve well upstream of the nozzle that is not suitable for smaller engines as explained previously.
Injectors for injecting fuel into the combustion chamber of an internal combustion engine have been known for many years. For example, the patents identified below disclose fuel injectors:
Baker U.S. Pat. No. 4,543,930 discloses an engine that includes a main fuel injector and a pilot fuel injector. The pilot and the main fuel may be the same fuel. The pilot injector injects from five to fifteen percent of the total fuel at different timings, depending upon the quantity of pilot fuel injected, the fuel cetane number and speed and load. The pilot fuel injector is directed toward the centerline of the diesel cylinder and at an angle toward the top of the piston. This avoids the walls of the cylinder. Stratification of the early injected pilot fuel is needed to reduce the fuel-air mixing rate, prevent loss of pilot fuel to quench zones and keep the fuel-air mixture from becoming too fuel lean to become effective. The pilot fuel injector can include a single hole for injection of the fuel and is directed at approximately 48 degrees below the head of the cylinder.
Wood U.S. Pat. No. 4,416,229 discloses a system whereby diesel fuel is supplied to the cavity of an injector at a location near the valve seat. Alternative fuel is supplied to the cavity of the injector. The diesel fuel is supplied at a relatively low pressure that does not move the valve member to the open position. The alternative fuel is supplied at a relatively high pressure which is sufficient to move the valve member to the open position at intervals just prior to the movement of the piston of the cylinder of the chamber into which the fuel is to be injected into high center position during its compression stroke. The fuel supply prevents the back flow of fuel, and thus maintains the cavity filled with fuel, except when alternative fuel is displaced within the cavity by the supply of diesel fuel. A plume of both fuels having the diesel fuel at its tip is injected into the chamber to enable the diesel fuel to be ignited by the compression in the chamber and the alternative fuel to be ignited by the diesel fuel.
Kelgard U.S. Pat. No. 4,742,801 discloses a dual fuel engine that is operated with straight diesel fuel or with gaseous fuel and pilot injection of diesel fuel. The Kelgard disclosure is primarily concerned with dual fuel engines for use in over the-road vehicles but it has other applications. The Kelgard disclosure also contemplates using the heat from the cooling water of the jackets of the engine to vaporize a liquid fuel into a gaseous state that is thereafter injected directly into the cylinders of the engine during operation on the dual fuel cycle.
Hill et al. U.S. Pat. No. 5,067,467 discloses a novel device for compressing and injecting gaseous fuel from a variable pressure gaseous fuel supply into a fuel receiving apparatus. The integrated intensifier-injector compresses and injects gaseous fuel from a variable pressure source into the cylinder of a positive displacement engine. The intensifier-injector for gaseous fuels in an internal combustion engine comprises a device which utilizes the compressed gas from the chamber of the internal combustion engine, or compressed fluid or gas from an external compressor, to drive an intensifier means which raises the pressure of fuel gas supplied to the internal combustion engine for rapid late-cycle injection into the cylinder of the internal combustion engine. In this device, gaseous fuel and liquid pilot fuel are mixed together and injected through the same holes.
Hill et al. U.S. Pat. No. 5,315,973 discloses a related device for compressing and injecting gaseous fuel from a variable pressure gaseous fuel supply into the fuel receiving apparatus. The intensifier-injector for gaseous fuels in an internal combustion engine comprises a mechanism which utilizes the compressed gas from an external compressor to drive an intensifier means which raises the pressure of fuel gas supplied to the internal combustion engine for rapid late-cycle injection into the cylinder of the internal combustion engine. In this device, the gaseous fuel and liquid pilot fuel are mixed together and injected through the same holes.
Tarr et al. U.S. Pat. No. 5,329,908 discloses a related fuel injector that has a gas accumulator having a volume that is at least ten times the volume of the maximum amount of fuel that would be injectable by the disclosed injector. A solenoid-operated poppet valve with an end face that opens into the combustion cylinder and is shaped to deflect a portion of the fuel injected into direct contact with the ignition plug is also disclosed. In a first embodiment, using a variable fuel supply, an electronic control unit (ECU) controls the injection timing to inject the compressed gas into the respective cylinders as each cylinder""s piston nears its top dead center position to obtain diesel engine-like efficiencies so long as the compressed gas supply pressure is sufficiently high. When the compressed gas supply pressure becomes too low for high efficiency operation, the ECU changes the manner of operation so that fuel is injected into the engine when the piston is near its bottom dead center position so that it can be premixed with air prior to ignition to produce gasoline engine-like efficiencies.
In summary, Baker U.S. Pat. No. 4,543,930 and Kelgard U.S. Pat. No. 4,742,801 employ two injectors. Wood U.S. Pat. No. 4,416,229, Hill et al. U.S. Pat. No. 5,067,467 and Hill et al. U.S. Pat. No. 5,315,973 inject the two fuels together. Tarr et al. U.S. Pat. No. 5,329,908 employs solenoid actuation of a gas injector only.
The Finnish work at Wartsila Diesel International pertains to the usage of directly injected natural gas with pilot diesel fuel and indicates the potential of the technology to use natural gas while retaining the high power output of diesel engines.
Wartsila Diesel International Oy of Finland owns the following patents and patent applications relating to dual fuel injectors:
1. European Patent Application No. 92305415.9, filed Jun. 12, 1992, entitled xe2x80x9cImproved Fuel Injection Valve Arrangement and Engine Using Such an Arrangementxe2x80x9d;
2. U.S. Pat. No. 5,199,398, filed Jun. 8, 1992, entitled xe2x80x9cFuel Injection Valve Arrangementxe2x80x9d;
3. European Patent No. 0778410, filed Jun. 12, 1996, entitled xe2x80x9cInjection Valve Arrangement for an Internal Combustion Enginexe2x80x9d;
4. European Patent No. 0787900, filed Jan. 28, 1997, entitled xe2x80x9cInjection Valve Arrangementxe2x80x9d;
5. European Patent No. 0718489, filed Jun. 12, 1996, entitled xe2x80x9cInjection Arrangement for an Internal Combustion Enginexe2x80x9d; and
6. U.S. Pat. No. 5,060,610, filed Sep. 21, 1990, entitled xe2x80x9cCombustion Process for Internal Combustion Engine Using Gaseous Fuelxe2x80x9d.
Nylund U.S. Pat. No. 5,199,398 and European Patent No. 0520659 Al disclose a fuel injection valve arrangement for so-called dual fuel engines using a pilot fuel needle and an axially movable, substantially hollow valve member permitting the injection of a gaseous fuel. The two needles are separately controllable.
European Patent No. 0778410 (Nylund) discloses an injection valve arrangement for an internal combustion engine using a pilot needle and at least two valves for the injection of the gaseous fuel. The pilot fuel injection is controlled externally to the injector, while a main valve controls the admitting of hydraulic fluid to actuate the gas needle injection valves.
European Patent No. 0718489 Al (Hellen) discloses an injection arrangement for an internal combustion engine using a pilot needle and a separately controllable valve for the injection of a different medium. The pilot fuel injection is controlled externally to the injector, while a main valve controls the admitting of hydraulic fluid to actuate the different medium injection valve.
European Patent No. 0787900 (Jay and Prillwitz) discloses an injection valve arrangement with two injection valves to inject an additional pressure medium into the combustion chamber of an internal combustion engine.
Nylund U.S. Patent No. 5,199,398, European Patent No. 0520659 Al, European Patent No. 0778410, European Patent No. 0718489 Al (Hellen) and European Patent No. 0787900 (Jay and Prillwitz) employ two different sources of fluid for the actuation of the usual liquid fuel and that of the additional fuel. Also, the metering of the liquid or pilot fuel is performed externally, rather than internally, to the injector.
U.S. Pat. No. 4,736,712 discloses a self-purging dual fuel injector that sequentially injects two fuels through the same series of holes. Because the same series of holes is used for both fuels, the fuels must have a similar density in order to maintain reasonable injection duration. The disclosed invention does not discuss the actuation of the needle used.
A dual fuel injector separately injects a first fuel and a second fuel into a combustion chamber of an internal combustion engine. The injector comprises:
(a) an injector body;
(b) a hydraulic fluid inlet port formed in the injector body for enabling pressurized hydraulic fluid from a hydraulic fluid source to be introduced into the interior of the injector body, the hydraulic fluid being of a pressure slightly above that of the gaseous fuel pressure within the injector body to maintain sealing and to prevent leakage of gaseous fuel into the hydraulic fluid;
(c) a first fuel inlet port formed in the injector body for enabling the first fuel to be introduced into the interior of the injector body;
(d) a first injection valve located within the injector body and fluidly connected to the first fuel inlet port for controlling injection of the first fuel from the injector through at least one first fuel ejection port or orifice;
(e) a second fuel inlet port formed in the injector body for enabling the second fuel to be introduced into the interior of the injector body;
(f) a second injection valve located within the injector body and fluidly connected to the second fuel inlet port for controlling injection of the second fuel from the injector through at least one second fuel ejection port or orifice;
(g) a first two-way control valve for controlling the flow of the hydraulic fluid to actuate the first injection valve;
(h) a second control valve for controlling the flow of the hydraulic fluid to actuate the second injection valve;
(i) a metering device located within the injector body for metering the amount of the first fuel injected by the first injection valve;
(j) an intensifier device located within the injector body for increasing the pressure of the first fuel; and
(k) a seal within the injector body for preventing leakage of the second fuel into the first fuel.
The first control valve is preferably electronically controlled and electrically operated. For example, in a preferred embodiment the first control valve is actuated by a solenoid that is electronically controlled and electrically operated. The second control valve may also be a two-way valve that is electronically controlled and electrically operated.
The two fuels injected by the dual fuel injector may be a pilot fuel that is used to initiate combustion and a main fuel that provides the majority of fuel to the engine. For example, when the first fuel is a pilot fuel, it may be a liquid fuel such as diesel that auto-ignites at a lower temperature and pressure than the main fuel. In a preferred embodiment, the main fuel is a high-pressure gaseous fuel, such as natural gas, propane, or hydrogen, that burns cleaner and produces less NOx and particulate matter than an equivalent amount of diesel fuel (on an energy basis). When the pilot fuel is a liquid fuel such as diesel, it can also be used as the hydraulic fluid since it can be readily supplied from the pilot fuel supply system.
A preferred arrangement of the injector employs a first injection valve that is a needle valve. A preferred embodiment of the needle valve injects the first fuel by using intensified pilot fuel pressure within the first injection valve to provide the opening force to lift the valve needle away from the valve seat so that the first fuel may be injected through the first fuel ejection port(s). The valve needle preferably lifts away from the valve seat into the needle valve body, however, the valve needle could also lift away from the valve seat in the direction of the combustion chamber (known as a poppet-style valve). The closing force is preferably provided by a spring, such as, for example, a mechanical coil spring.
The second injection valve is also preferably a needle valve. In one preferred embodiment, high-pressure hydraulic fluid is directed to a hydraulic fluid chamber associated with the second injection valve to provide the closing force. When the hydraulic fluid is drained from the hydraulic fluid chamber, the pressure of the second fuel within a cavity of the injector body acts on the valve needle to provide the opening force to lift the valve needle away from the valve seat of the second injection valve. In an alternative embodiment, a spring is used to provide the closing force and the high-pressure hydraulic fluid is directed to a chamber associated with the second injection valve to apply the opening force. In this alternate embodiment the second injection valve returns to the closed position when the hydraulic fluid is drained from the hydraulic fluid chamber.
The seal provided within the injector body is preferably a fluid seal that comprises hydraulic fluid disposed within a cavity within the injector body. The seal operates to prevent leakage of the second fuel by filling the cavity with a hydraulic fluid that has a pressure that is higher than the pressure of the second fuel. The cavity is formed between the injector body and the needle of the second injection valve and prevents the second fuel from leaking through the gap between the injector body and the moveable valve needle. The hydraulic fluid used to fill the fluid seal is preferably the same hydraulic fluid that is employed to actuate the first and second needle valves.
In a preferred arrangement of the injector the first needle valve and the second needle valve are concentric with the first needle valve being the inner valve and the second needle valve being disposed in the annular space around the first needle valve. In this arrangement, the body of the first needle valve preferably acts as the needle for the second needle valve. In this arrangement, the second fuel is ejected through ports located in the tip of the injector body, and the first fuel is ejected through ports located in the tip of the second needle valve.
The metering device is preferably integral with the intensifier device. In a preferred embodiment the intensifier comprises a piston disposed within a cylinder with one side of the piston facing a chamber that may be filled with high-pressure hydraulic fluid and the other side of the piston facing a chamber that is in fluid communication with the fluid passages that supply the first fuel to the first injection valve. The first fuel is metered by the amount of fuel that is drawn into the fuel chamber associated with the intensifier piston. This amount is determined by the movement of the piston and how far it moves to expand the volume of the fuel chamber. The pressure of the first fuel is intensified when high-pressure hydraulic fluid is directed into the chamber on the opposite side of the piston, causing the piston to move to expand the volume of the hydrualic fluid chamber and to reduce the volume of the fuel chamber. Thus the fuel within the fuel chamber is compressed, intensifying the pressure of the first fuel in the fluid passages and within the first injection valve. A one-way check valve prevents the pressurized first fuel from escaping to the fluid passages upstream of the intensifier. When the hydraulic fluid is drained from the hydraulic fluid chamber associated with the intensifier piston, the piston moves to reduce the volume of the hydraulic fluid chamber while drawing another another metered charge of first fuel into the fuel chamber for the next injection event. In this way, instead of using the hydraulic fluid to directly control the first injection valve, the hydraulic fluid is employed to actuate the intensifier, which in turn elevates the pressure of the first fuel to operate the first injection valve.
In another embodiment of the injector, the intensifier piston acts as a three-way valve for admitting and draining hydraulic fluid from a hydraulic actuation chamber for the second injection valve.
Another embodiment of a liquid and gaseous fuel injector for separately injecting a liquid fuel and a gaseous fuel into a combustion chamber of an internal combustion engine comprises:
(a) an injector body having formed therein:
at least one hydraulic fluid inlet port for admitting hydraulic fluid into hydraulic fluid passages disposed within the interior of the injector body;
a liquid fuel inlet port;
a gaseous fuel inlet port; and
at least one drain port for draining hydraulic fluid from the injector body;
(b) a liquid fuel injection valve that is maintainable in a closed position by a spring and that is openable to inject liquid fuel into the combustion chamber when liquid fuel pressure within the liquid fuel injection valve is sufficient to provide an opening force that overcomes the closing force applied by the spring, wherein hydraulic fluid pressure is employed to control the liquid fuel pressure;
(c) a first hydraulic actuator system for controlling the liquid fuel pressure within the liquid fuel injection valve, the first hydraulic actuator system comprising:
a first hydraulic fluid chamber, wherein the liquid fuel pressure is controlled by controlling the hydraulic fluid pressure within the first hydraulic fluid chamber;
a first hydraulic fluid passage fluidly connected to the first hydraulic fluid chamber, wherein a two-way valve is employed to control the flow of hydraulic fluid through the first hydraulic fluid passage; and
a second hydraulic fluid passage fluidly connected to the first hydraulic fluid chamber, wherein an orifice is employed to control the flow of hydraulic fluid through the second hydraulic fluid passage wherein one of the first and second hydraulic fluid passages is fluidly connected to the at least one hydraulic fluid inlet port and the other one of the first and second hydraulic fluid passages is fluidly connected to the at least one hydraulic fluid drain port;
(d) a gaseous fuel injection valve for controlling the injection of the gaseous fuel through the gaseous fuel injection port and into the combustion chamber, the gaseous fuel injection valve being hydraulically actuated by a second hydraulic actuator system that is in fluid communication with at least one of the hydraulic fluid passages within the injector body; and
(e) a seal preventing leakage of the gaseous fuel within the injector body.
The liquid and gaseous fuel injector may further comprise a metering device for metering the amount of liquid fuel that is directed to the liquid fuel injection valve. The metering device may comprise, for example, a piston disposed within a cylinder. The hydraulic fluid pressure within the first hydraulic fluid chamber is applied to one side of the piston and the metered liquid fuel within a fuel chamber on the other side of the piston is compressed when the piston moves to reduce the volume of the fuel chamber, thereby intensifying the pressure of the metered liquid fuel.
The liquid and gaseous fuel injector preferably comprises a gaseous fuel injection valve that is operable between an open position and a closed position by elevating the hydraulic fluid pressure within a second hydraulic fluid chamber. In addition, the liquid and gaseous fuel injector may further comprise a second hydraulic actuator system for controlling the hydraulic fluid pressure within the second hydraulic fluid chamber. For example, the second hydraulic actuator system may comprise:
a third hydraulic fluid passage fluidly connected to the second hydraulic fluid chamber, wherein a two-way valve is employed to control the flow of hydraulic fluid through the third hydraulic fluid passage; and
a fourth hydraulic fluid passage fluidly connected to the second hydraulic fluid chamber, wherein an orifice is employed to control the flow of hydraulic fluid through the fourth hydraulic fluid passage;
wherein one of the third and fourth hydraulic fluid passages is fluidly connected to the at least one hydraulic fluid inlet port and the other one of the third and fourth hydraulic fluid passages is fluidly connected to the at least one hydraulic fluid drain port.